Modal Operators Timing/Profiling

Question

Trying to get a feeling for the timing of Modal Operators I did some experiments and need some advice on how to interpret them

I experimented with this script

import bpy
import time
class ModalTimerOperator(bpy.types.Operator):
    """Operator which runs its self from a timer"""
    bl_idname = "wm.modal_timer_operator"
    bl_label = "Modal Timer Operator"
_timer = None

def modal(self, context, event):
    if event.type in {'RIGHTMOUSE', 'ESC'}:
        self.cancel(context)
        return {'CANCELLED'}

    if event.type == 'TIMER':
        print((time.time_ns() - self.old_time)/1.0e9)
        while self.i < 10:
            self.i += 1
        self.i = 0
        self.old_time = time.time_ns()
    return {'PASS_THROUGH'}

def execute(self, context):
    wm = context.window_manager
    self._timer = wm.event_timer_add(0.01, window=context.window)
    wm.modal_handler_add(self)
    self.old_time = time.time_ns()
    self.i = 0

    return {'RUNNING_MODAL'}

def cancel(self, context):
    wm = context.window_manager
    wm.event_timer_remove(self._timer)



def register():
    bpy.utils.register_class(ModalTimerOperator)
def unregister():
    bpy.utils.unregister_class(ModalTimerOperator)
if name == "main":
    register()
test call
bpy.ops.wm.modal_timer_operator()

on my machine the minimum timing for the timer is 10ms

I then timed the while loop in the execute method of the operator

8s for counting to 1 000 000

0.8 for 100 000

0.1 for 10 000

0.01 for 1 000

0.002 for 100

0.001 for 10

OK, consistent

then I put the while loop in the modal method (as in the script above)

as long as the execution time of the while loop is less than the frequency of the timer everything is fine.

But as soon as the execution time is larger than the frequency the print statement starts to print additional 0.0!

WHY?

What is the scheduler doing?

THX Martin